Expansible bolt anchoring devices are widely used in the construction industry for attaching articles to rigid structures constructed of, for example, concrete, masonry, or brick. These rigid structures may include walls, ceilings, floors, and the like made of such rigid substrate materials as mentioned above. A conventional expansible type anchor device typically includes a segmented expansible sleeve, an expansion bolt, and an expansion member. The expansion member may be in the form of a nut on the bolt (such as in a “loose bolt” anchor) or may form the head of the bolt (such as in a “projecting bolt” anchor). The expansion member is initially positioned at the inner end of the segmented shell such that rotation of the bolt, or rotation of a nut on the shank of the bolt, will draw the expansion bolt into the sleeve and radially expand the sleeve. Thus, when the device is located in a hole having a diameter substantially similar to the diameter of the segmented sleeve, tightening the bolt or nut expands the sleeve radially to engage the walls of the hole.
To prevent the bolt from simply spinning in the hole, and hence actually tightening the bolt or nut in the hole, it is required that a portion of the sleeve engage the hole wall to restrict the rotational movement of the anchor within the hole. This requires that the sleeve have a snug fit in the hole, which is often difficult to achieve because of various manufacturing tolerances in the bolts and inexact hole diameters from drilling. In the absence of such a close fit, the sleeve must be held or constrained in the hole by some other means, such as filling the hole with some type of packing material.
The three or four segments that typically form the sleeve of conventional expansible anchors are formed of pressed metal. An example of this type of anchor can be seen in U.S. Pat. No. 4,656,806 (the '806 patent). The bolt taught in the '806 patent has a cone shape on one end such that when the nut is tightened, the sleeve is forced over the cone, which in turn creates radial pressure on the wall of the hole. However, because the sleeve of this bolt tends to engage the wall at a single point of contact, a large amount of pressure is exerted on the single point of contact, which often leads to a crushing effect occurring to the rigid substrate material. Further, because these rigid substrate materials are frequently softer than the metal of the expansible sleeve, the crushing effect continues as the expansion member is further tightened leading to large-scale failures. These failures are particularly dangerous because the bolt may initially appear to be secure if the crushing happens below the outside surface of the material, and the anchor may fail only after a large force is later exerted on it.
Expandable anchor failure in these rigid materials may pose an even greater problem when they are used in tensile zones subject to fracture, such as joints where bricks or blocks are mortared together.
Several devices using resilient sleeves have been proposed to help overcome the crushing problem in masonry and brick applications, such as in U.S. Pat. Nos. 4,472,008 and 6,273,655. However, these devices are overly complex and expensive to manufacture. Further, they are difficult to place and set, and they can be almost impossible to remove for later use. Consequently, they have not been adopted by the construction industry. These and other problems in the conventional art are addressed by embodiments of the present invention.